1. Field of the Invention
The present invention relates to low NO.sub.x gas burner apparatus and methods for burning fuel gas-air mixtures whereby flue gases having low NO.sub.x content are produced.
2. Description of the Prior Art
More stringent environmental emission standards are continuously being imposed by governmental authorities which limit the quantities of gaseous pollutants such as oxides of nitrogen (NO.sub.x) and carbon monoxide which can be emitted into the atmosphere. Such standards have led to the development of various improved gas burner designs which lower the production NO.sub.x and other polluting gases. For example, methods and apparatus wherein fuel is burned in less than a stoichiometric concentration of oxygen to intentionally produce a reducing environment of CO and H.sub.2 have been proposed. This concept has been utilized in staged air burner apparatus wherein the fuel is burned in a deficiency of air in a first zone producing a chemically reducing environment that suppresses NO.sub.x formation, and the remaining portion of air is introduced into a second oxidizing zone.
Methods and apparatus have also been developed wherein all of the air and some of the fuel is burned in a first zone and the remaining fuel is burned in a second zone. In this staged fuel approach, an excess of air in the first zone acts as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NO.sub.x. Other methods and apparatus have been developed wherein flue gases are combined with fuel gas and/or fuel gas-air mixtures to dilute the mixtures and lower their combustion temperatures and the formation of NO.sub.x.
While the prior art methods and burner apparatus for producing flue gases having low NO.sub.x content have achieved varying degrees of success, there still remains a need for improvement in gas burner apparatus and methods of burning fuel gas whereby simple economical burner apparatus is utilized and low NO.sub.x content flue gases are produced.